Magnetic Field Dependence of Ultrafast Intersystem-Crossing: A Triplet Mechanism on the Picosecond Time Scale?

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• 作者：Christian Musewald ; Peter Gilch ; Gerhard Hartwich ; Florian Pö ; llinger-Dammer ; Hugo Scheer ; and Maria Elisabeth Michel-Beyerle
• 刊名：Journal of the American Chemical Society
• 出版年：1999
• 出版时间：September 29, 1999
• 年：1999
• 卷：121
• 期：38
• 页码：8876 - 8881
• 全文大小：78K
• 年卷期：v.121,no.38(September 29, 1999)
• ISSN：1520-5126

文摘

The influence of strong magnetic fields up to 9 T on the decay kinetics of Ni²⁺-bacteriochlorophylla was studied by femtosecond pump-probe spectroscopy. The appearance of a magnetic field effect dependson the initial electron spin state of the molecule, which can be switched by using suitable solvents. In toluene,where the central Ni²⁺ is tetracoordinated, the ground state has singlet multiplicity, while in pyridine, wherein addition two solvent molecules bind to the Ni²⁺ ion, it is a paramagnetic triplet state. In toluene, no fielddependence of the excited-state decay kinetics is observed, whereas in pyridine the decay is accelerated bystrong magnetic fields, on a time scale of 10 ps. The field-dependent process has been identified as a loss ofaxial pyridine ligands which is accompanied by intersystem crossing to a singlet state. The field dependenceis discussed in terms of a triplet mechanism, which is applicable if an electron spin relaxation time of 100ps and a large zero-field splitting of ~20 cm^-1 are assumed.